This invention relates to wood burning heating units and fireplaces. More particularly, the present invention relates to a wood burning assembly that is designed to minimize the exhaust of unburned gases and reduce particulate emission.
Wood burners are desirable features in the home. However, for many years, in response of an increased population density in certain areas and increased environmental concerns, wood burners, such as wood-burning fireplaces and heaters have been increasingly regulated with respect to particulate and other emissions.
In recent years the quality of the air has received major consideration. Clean air has become more than a phrase. Significant efforts have been expended to minimize pollutants in the air we breathe. Some examples of these efforts include imposing emission standards on automobile exhausts, shutting down the use of incinerators in apartment houses, and designing or modifying large garbage burning incinerators to meet established standards.
Several of the compounds produced during the combustion of wood are of great concern to environmentalists and to environmental organizations, such as the Federal Government""s Environmental Protection Agency (EPA), interested in maintaining, or in some cases establishing, clean air. The problem of air pollution caused by the compounds produced when wood burns has been recognized by many, and a growing number of state and local environmental agencies are considering the regulation of wood burning devices.
As a result of this concern, for example, emission standards for a majority of combustion processes have been established by the EPA. On Feb. 18, 1987, the Environmental Protection Agency (EPA) published in the Federal Register, Volume 52, No. 32, 40 CFR Part 60 entitled xe2x80x9cStandards of Performance for New Stationary Sources, Standards of Performance for New Sources, Residential Wood Heaters.xe2x80x9d These regulations were proposed to control the burgeoning wood stove and fireplace industry, which many believed was substantially adding to the air pollution problem in the United States. These pollutants are varied and many. The primary pollutants include particles of organic compounds, carbon monoxide, volatile organic compounds, and nitrous oxides.
A widespread lack of effective emission reduction devices and methods for many fireplaces and other wood burners has prompted agencies and governments in some areas of the country where emissions from wood burning units are increasingly problematic, to ban their use in times of air pollution. Overall, the number of days during which wood burning is banned is increasing, as are the number of communities that ban their use.
Several emission reduction devices have been suggested in the art. One such fireplace pollutant removal device of the prior art utilizes a filter, a fan, and a smoke detector. In operation, the filter is placed in the flue, the fan is positioned above the filter to draw the exhaust gases up through the filter, and the smoke detector is mounted in front of the fireplace. The smoke detector acts as a monitor of gases reflected from a clogged filter and provides an alarm when the filter needs cleaning. A method of removing the clogged filter provides a roll of thin filter-paper which is scrolled through the flue as segments of the filter-paper saturate with pollutants. This method, however, has perceived drawbacks. For instance, if the paper clogs, smoke may be emitted from the fireplace into the area adjacent to the wood burning chamber.
Another fireplace pollutant filter of the prior art utilizes a ceramic fiber duct positioned, along the flow path of the combustion products, between the combustion chamber and the flue. A first duct portion promotes secondary combustion of unburned products of combustion and a second duct portion directs products of combustion from the front of the combustion chamber to the flue. Though this device may remove some pollutants by the secondary combustion, many may enter the atmosphere due to an incomplete removal by the secondary combustion.
Although there are many catalytic devices designed to reduce pollutants in fluid streams, the backpressures created by these devices can be a design issue. The increased backpressure hinders the fireplace""s draw, causing a variety of potential unacceptable consequences, including smoke backing up into the house under certain conditions. Several companies have produced catalytic secondary combustion chambers to reduce the amount of pollution, which while effective, nonetheless substantially increased the cost of the stove.
It is possible to produce a wood burner operating at a very high temperature that creates a condition to substantially reduce the amount of particulate material and air pollutants being emitted from wood burning. However, wood burners having a large firebox volume are more difficult to design in a cost-effective way to reduce particulates and emissions to meet EPA requirements. The problem lies, at least in part, in the difficulty of maintaining high combustion temperatures in all areas within the firebox, and especially when the unit is operated at a slow burn rate.
There is a demand therefore for a wood burner that meets requirements of the EPA emissions regulations. The present invention satisfies the demand.
The present invention has a principal objective of providing a wood burner having a large combustion chamber volume with a configuration and mechanism for clean burning.
Broadly stated, this is accomplished by providing a novel shape of firebox, which reduces or substantially eliminates cold spots in the combustion chamber, and concentrates heat in the center of the chamber. The thermal mass of the firebox is situated to both initiate pyrolisis (baking the combustion gases from the fuel for use in secondary combustion) and maintain elevated temperatures with the combustion chamber to continue efficient combustion of gases. In addition, a novel manifold/upper refractory panel and air supply arrangement is provided, which when used in combination, uses both exhaust and combustion heat in order to preheat secondary air in the manifold and the upper refractory panel. The manifold includes manifold tubes positioned adjacent the upper refractory panel, which panel includes a novel waveform adapted to direct radiant stored heat into the tubes. Further, a metered primary air inlet and primary air nozzle uses a predetermined orifice diameter to precisely meter incoming air at a variety of settings. In particular, the primary nozzle meters a predetermined flow of air into the combustion chamber when the primary air inlet is set at a slow burn setting. In this manner, the wood burner is clean burning, i.e., emits an acceptable minimal amount of regulated pollutants at a variety of burn rates.
One aspect of the invention provides a wood heater that includes a wrapper. A firebox is positioned in the wrapper defining a combustion chamber. A primary air inlet receives external air. The primary air inlet includes a first conduit to conduct the external air to the combustion chamber and a secondary air inlet for receiving external air including a secondary conduit. A manifold is positioned above the firebox in communication with the secondary conduit. The manifold includes one or more manifold chambers for permitting the external air received thereby to become heated. A plurality of air tubes connected to the manifold receives the heated external air from the manifold. Each of the plurality of air tubes including a plurality of apertures to direct the heated external air into the combustion chamber adjacent an upper inner surface of the firebox.
In other aspects of the invention the firebox may include a lining defining a combustion chamber. The first conduit may include a primary air nozzle having an orifice in communication with the combustion chamber, the orifice having a predetermined diameter to supply a predetermined airflow to the combustion chamber when the wood heater is operated in a slow burn mode. A major portion of the combustion chamber may comprise a rectangular volume. The lining may be comprised of a refractory material. The lining may include a lower refractory panel, a pair of side refractory panels, a rear refractory panel and an upper refractory panel. Each of the pair of side refractory panels may include a convex section extending into the combustion chamber. Each of the pair of side refractory panels may include a concave portion adjacent a rear corner of the combustion chamber wherein each of the pair of side refractory panels abuts a similarly convex portion of the rear refractory panel. The manifold may be positioned above the upper refractory panel and includes one or more inlet for receiving outside air, one or more manifold chamber defined within the manifold in which the temperature of the received air is elevated, and one or more manifold tube positioned in the combustion chamber adjacent an underside surface of the upper refractory panel, the one or more manifold tube being in communication with the one or more manifold chamber and having manifold apertures to conduct the heated air into the combustion chamber. The underside of the upper refractory panel may include a plurality of ramps, each of the one or more manifold tube being positioned between an adjacent pair of the ramps.
Another aspect of the present invention has the firebox positioned in the wrapper, with the firebox comprised of a lining including a lower refractory panel, a pair of side refractory panels, a rear refractory panel and an upper refractory panel. The upper refractory panel includes an underside surface positioned toward the combustion chamber, the underside including a plurality of transverse ramps. A manifold is positioned above the upper refractory panel. The manifold includes one or more inlets for receiving outside air, one or more manifold chambers defined within the manifold in which the temperature of the received air is elevated, and one or more manifold tubes positioned in the combustion chamber adjacent the underside surface, the one or more manifold tubes being in communication with the one or more manifold chambers each having manifold tube apertures to conduct the heated air into the combustion chamber.
Other aspects of the present invention provide a wood heater wherein the manifold further includes a manifold cover. The one or more inlets are connected to the manifold cover and are in communication with outside air to convey the outside air through the manifold cover. A diverter plate may be connected to the manifold cover and spaced therefrom to define therewith a first manifold chamber. The diverter plate may include one or more manifold apertures. A manifold cap may be connected to the diverter plate and spaced therefrom to define therewith a second manifold chamber to receive air from the first manifold chamber through the manifold apertures. The manifold cap may have corrugations that define one or more transverse manifold channels therebetween, each of the one or more manifold channels being aligned with each of the one or more manifold apertures. The one or more manifold tubes are in communication with one of the one or more manifold channels.
Another aspect of the invention provides a lining for a wood burner firebox including a bottom refractory panel including a back edge. A back refractory panel includes a lower edge, the lower edge abutting the bottom refractory panel at the back edge. The back refractory panel includes left and right corners. The left and right corners include concave sections. A pair of side refractory panels abuts the back refractory panel at the left and right corners. The pair of side refractory panels include a convex section to define with the back refractory panel a generally rectangular combustion chamber including arcuate convex left and right rear corners.
Other aspects of the present invention further provide an upper refractory panel including an underside surface. The upper refractory panel may include one or more transverse ramp portions. Each of the one or more ramp portions may include an angled side and a low-angled side. Each of the one or more ramp portions may include one or more slots oriented perpendicular to a length of the ramp portions.
These and other advantages, as well as the invention itself, will become further apparent in the details of construction and operation as more fully described below. Moreover, it should be appreciated that several aspects of the invention can be used in other applications where non-wood combustibles are used.